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1 January 2010 Effects of Lipid Extraction on Stable Isotope Ratios in Avian Egg Yolk: Is Arithmetic Correction a Reliable Alternative?
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Many studies of nutrient allocation to egg production in birds use stable isotope ratios of egg yolk to identify the origin of nutrients. Dry egg yolk contains >50% lipids, which are known to be depleted in 13C. Currently, researchers remove lipids from egg yolk using a chemical lipid-extraction procedure before analyzing the isotopic composition of protein in egg yolk. We examined the effects of chemical lipid extraction on δ13C, δ15N, and δ34S of avian egg yolk and explored the utility of an arithmetic lipid correction model to adjust whole yolk δ13C for lipid content. We analyzed the dried yolk of 15 captive Spectacled Eider (Somateria fischeri) and 20 wild King Eider (S. spectabilis) eggs, both as whole yolk and after lipid extraction with a 2:1 chloroform:methanol solution. We found that chemical lipid extraction leads to an increase of (mean ± SD) 3.3 ± 1.1‰ in δ13C, 1.1 ± 0.5‰ in δ15N, and 2.3 ± 1.1‰ in δ34S. Arithmetic lipid correction provided accurate values for lipid-extracted δ13C in captive Spectacled Eiders fed on a homogeneous high-quality diet. However, arithmetic lipid correction was unreliable for wild King Eiders, likely because of their differential incorporation of macronutrients from isotopically distinct environments during migration. For that reason, we caution against applying arithmetic lipid correction to the whole yolk δ13C of migratory birds, because these methods assume that all egg macronutrients are derived from the same dietary sources.

© 2010 by The American Ornithologists' Union. All rights reserved. Please direct all requests for permission to photocopy or reproduce article content through the University of California Press's Rights and Permissions website,
Steffen Oppel, Rebekka N. Federer, Diane M. O'Brien, Abby N. Powell, and Tuula E. Hollmén "Effects of Lipid Extraction on Stable Isotope Ratios in Avian Egg Yolk: Is Arithmetic Correction a Reliable Alternative?," The Auk 127(1), (1 January 2010).
Received: 12 June 2008; Accepted: 1 May 2009; Published: 1 January 2010

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